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This Article describes research on chemical reactions on molecules attached to the surface of silicon quantum dots that have been performed to produce quantum dots with reactive surface functionalities such as diols and epoxides. Characterization of the surface reactions includes NMR and FT-IR studies, and the quantum dots were characterized by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). Cytotoxicity and cell viability assay conducted on silicon dots capped with polar molecules indicated low toxicity with quantum dots with more reactive functionalities found to be more toxic. The silicon quantum dots photoluminesce and have been used as a blue chromophore for the biological imaging of cells.

Germanium nanocrystals were synthesized by the hydride reduction of germanium tetrachloride (GeCl 4 ) in inverse micelles using hydride reducing agents including lithium aluminum hydride (LiAlH 4 ), lithium triethyl borohydride (Li(C 2 H 5 ) 3 BH), lithium borohydride (LiBH 4 ), and sodium borohydride (NaBH 4 ). Monodisperse Ge nanocrystals with average sizes ranging from 4.0 to 5.5 nm were produced using a simple room temperature technique. The nanocrystals were capped using allylamine. The nanocrystals displayed strong blue luminescence, and their application as optical probes is demonstrated by the imaging of HepG2 cells. Transmission electron microscopy (TEM), selected area electron diffraction (SAED), energy dispersive X-ray spectroscopy (EDX), and fluorescence spectroscopy were used to characterize the nanocrystals. The cytotoxicity of the nanocrystals is also reported, and the germanium quantum dots were found to be relatively nontoxic.

Semiconductor quantum dots (QDs) hold some advantages over conventional organic fluorescent dyes. Due to these advantages, they are becoming increasingly popular in the field of bioimaging. However, recent work suggests that cadmium based QDs affect cellular activity. As a substitute for cadmium based QDs, we have developed photoluminescent stable silicon quantum dots (Si-QDs) with a passive-oxidation technique. Si-QDs (size: 6.5 ± 1.5 nm) emit green light, and they have been used as biological labels for living cell imaging. In order to determine the minimum concentration for cytotoxicity, we investigated the response of HeLa cells. We have shown that the toxicity of Si-QDs was not observed at 112 µg ml(-1) and that Si-QDs were less toxic than CdSe-QDs at high concentration in mitochondrial assays and with lactate dehydrogenase (LDH) assays. Especially under UV exposure, Si-QDs were more than ten times safer than CdSe-QDs. We suggest that one mechanism for the cytotoxicity is that Si-QDs can generate oxygen radicals and these radicals are associated with membrane damages. This work has demonstrated the suitability of Si-QDs for bioimaging in lower concentration, and their cytotoxicity and one toxicity mechanism at high concentration.